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The Hunshandake Sandy Lands of northeastern China, currently a semiarid lightly vegetated region, were characterized by perennial lakes and forest stands in the early and middle Holocene. Well-developed dark grassland-type paleosols (mollisols) at the southern edge of the Hunshandake – OSL (optically stimulated luminescence)-dated to between 6.93±0.61 and 4.27±0.38 ka along with lacustrine sands at higher elevations that date to between 5.7±0.3 and 5.2±0.2 ka – and thick gray lacustrine sediments suggest a wetter climate. Between 4.2 and 3.8 ka, the region experienced extreme drying that was exacerbated by lake overflow drainage and sapping that depleted the groundwater table. The region supported a robust population, the Hongshan Culture, but was depopulated post 4.2 ka with migration likely to the Yellow River Valley where the Hongshan introduced their characteristic cultural elements to early Chinese civilization. Evidence for extreme and sudden environmental change in northeastern China, at and following the 4.2 ka BP Event and like that we document in the Hunshandake, is widespread. However, no comprehensive overview of this climatic episode exists. Here, we discuss the relevant events in northeastern China and capture them in a spatially explicit Geographic Information Systems database that can be used to analyze the timing and spatial pattern of climate and environmental change associated with the 4.2 ka BP Event. This approach could serve as a prototype for a global 4.2 ka BP Event database. [ABSTRACT FROM AUTHOR]

Abstract: Characterization of dune morphology has historically been based on relationships between dune forms and wind regimes with dune height shown to be sensitive to atmospheric boundary layer depth, sand availability and sediment properties. While these parameters have been used in numerical simulations to model the occurrences of some types of dunes, they cannot alone explain the great diversity in form and size seen on Earth and on other solar system bodies. Here we present results from our studies of dune formation in the Badain Jaran Desert in western China, where Earth''s tallest dunes occur. We measured the variability of the dune morphology in this desert on the basis of LANDSAT ETM+ data, and we detected the bedrock landforms beneath the aeolian sands by applying gravity methods. Wind records from stations at the periphery of the desert and SRTM topographical data were examined also to augment the interpretation. Our studies demonstrate that in addition to average wind parameters, dune height is highly sensitive to local geology, subsurface characteristics, and topography, and interactions between changing climate conditions and aeolian and fluvial processes. These additional factors need to be considered in the interpretation and simulation of dunes on Earth. We anticipate that analysis of anomalous dune heights like those seen in the Badain Jaran may also provide critical information on subsurface characteristics and environmental conditions on Earth and on other planetary bodies. [Copyright &y& Elsevier]

Abstract: The formation of cracks is a fundamental first step in the physical weathering of rocks in desert environments. In this study we combine new field data from the Mojave (U.S.), Gobi (Mongolia) and Strzelecki (Australia) deserts that collectively support the hypothesis that meridional cracks (cracks with orientations not readily attributable to rock anisotropies or shape) in boulders or cobbles form due to tensile stresses caused by directional heating and cooling during the sun''s daily transit. The new studies indicate that rock size, surface age, and latitude play important roles with respect to their influence on rock fracture. Rock size and pavement surface age exert an influence on the development of rock cracks as the average clast size of mature desert pavements may be at or below the threshold-clast size for thermal cracking of rocks. Latitude-controlled seasonal temperature variations play a key role, as demonstrated by: 1) tightly clustered mean resultant orientations that differ by latitude, as predicted in McFadden et al. (2005), and 2) very cold wintertime temperatures and strong diurnal gradients that may favor crack development in wintertime, given the likelihood for strong clast heating during early morning hours. The consistent evidence for meridional cracks in surfaces of diverse age and desert environments, climate, vegetation, and distance of clast transport indicate that directional insolation may play the key role in initially generating and propagating rock fractures, rather than a secondary role as implied in recent field and modeling studies of physical weathering in deserts. [Copyright &y& Elsevier]